Wastewater Is Tracking Down COVID In Communities

For years, public health researchers have known viruses show up in a human's stool. But COVID amped up funding and interest to invest in a network.
Posted at 10:45 PM, Mar 16, 2022

What happens in the bathroom brings important data to the CDC's control center during the COVID-19 pandemic.  

Wastewater, nationwide, carries clues on what to expect next from COVID. It accurately detects the virus in the community before it shows up clinically in cases or hospitalizations. 

But it isn't as simple as bathroom door closed ... to blip on the CDC data tracker. There are many steps with many players, and the first part involves collections. 

Sandra Macomb runs a small team responsible for sewer surveillance sample collections in Davis, California. 

"We have 24 collection sites in the city of Davis," she said. "We collect every Monday, Wednesday, Friday."

She's pulls a large collector barrel from below ground.  

"So here we're at the bottom part," Macomb said. "And as you see, we have a plastic bag liner, so every day is a clean sample."

A large pipette with vacuum-sealed sterile suction assures no outside particles cross-contaminate the specimen. 

There's already extra variability here: liquid samples are literally watered down by sources like rain.  

Across town, wastewater treatment plant operator Peter Sprague readied two wastewater samples for a lab. One is liquid. The other is called sludge, which scientists call settled solids. It smells exactly how you think it'd smell. 

But some researchers prefer it. The viral particles in sludge are more concentrated.  

"The process of getting the solids or the liquids out of the sewage and extracting the RNA from that and doing virus detection are slightly different," Dr. Alexandria Boehm said.   

Boehm runs a team of researchers that are part of a network that analyzes wastewater from San Jose to Sacramento, California. She also examines samples from around the country.  

Bringing us to the step after collections in the field: Extractions in the lab.  

One lab at UC Berkeley is part of the National Wastewater Surveillance System, a network that the CDC started back in September of 2020. The whole goal of the network is to better track the Sars-CoV-2 virus. 

All the researchers monitoring wastewater are after the same thing. They’re trying to measure the concentration of RNA, which is a genetic ID tag of sorts. The higher the concentration, the more virus there is circulating.  

To get that good data, scientists pour the samples through a tiny column with silica beads in it.  

The RNA sticks to the beads through electrostatic attraction — the same mechanism that makes a balloon stick to your shirt after your rub it on your head. 

The rest of the wastewater flows through, with that RNA concentrate left over. Another solution, some pipetting and what's left is a clear liquid that has all the RNA and DNA from the wastewater sample.

That's then run through a hypersensitive PCR test to see if the extracted RNA in that tiny vial is the Sars-CoV-2 RNA. 

Wastewater is analyzed by trends, not daily counts. 

"You can have a sample one day that is particularly high or quite low and deviate from what you expect," Boehm said. "And it doesn't mean necessarily that there's been a huge change in COVID-19 incidence." 

But it's those data trends that now make its way to the public dashboard. 

And then the last step along the way in our public lives. Public health officials make those decisions from all the science and data to decide what we need to do to be safe in this time of COVID. 

In Davis, which is a community of 60,000, their surveillance is down to a neighborhood level. The city can text people in specific areas if cases trend up.  

"We want to do that sparingly. We don't want to cry wolf. Essentially, that's why we're looking at the data and you know what looks to be a sustained and significant change," UC Davis Environmental Engineer and Researcher Heather Bischel said. 

It's a system that again, is being put to the test.  

Omicron's subvariant, BA.2, is showing up in wastewater surveillance. 

It's about 30% more transmissible that its parent Omicron strain. And experts think it will cause a late spring wave.  

"Wastewater is really great because it's agnostic of behaviors around testing, around willingness, around costs, access, affordability," said American Federation of Scientists Epidemiologist Dr. Eric Feigl-Ding.  

It's not hard to see why scientists are a fan. Wastewater is passive, anonymous and full of public health answers.